FXUS62 KRAH 130712
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
310 AM EDT WED APR 13 2011
.SYNOPSIS...
AN UPPER LEVEL LOW PRESSURE AREA WILL DRIFT OVERHEAD THIS MORNING
AND DEPART TO THE NORTHEAST LATER TODAY. WEAK HIGH PRESSURE WILL
BUILD IN FROM THE WEST WEDNESDAY NIGHT THROUGH THURSDAY NIGHT... AND
SHIFT OFF THE COAST FRIDAY. A STORM SYSTEM WILL APPROACH FROM THE
WEST FRIDAY NIGHT.
&&
.NEAR TERM /TODAY THROUGH TONIGHT/...
AS OF 240 AM WEDNESDAY...
THE STACKED LOW OVER CENTRAL VA THIS MORNING WILL MOVE TOWARD THE
NNE OVER ERN PA TODAY BEFORE WEAKENING TO AN OPEN WAVE AND CROSSING
NEW ENGLAND AND CANADIAN MARITIMES TONIGHT. SURFACE LOW PRESSURE
LOCATED JUST EAST OF THE MID LEVEL VORTEX... OVER EASTERN VA
ACCORDING TO THE LATEST SURFACE ANALYSIS... HAS A WEAK SURFACE
TROUGH EXTENDING DOWN THROUGH CENTRAL NC EARLY THIS MORNING (ONE OF
SEVERAL TROUGHS ROTATING ABOUT THE SURFACE LOW). AS THIS LOW ALSO
TRACKS TO THE NNE AWAY FROM NC... CYCLONIC SURFACE FLOW WILL BECOME
UNIFORM NORTHWESTERLY ACROSS THE AREA THIS MORNING... INITIALLY A
BIT BREEZY AND GUSTY WITH A DECENT MSLP GRADIENT ACROSS THE STATE...
HOWEVER THIS WILL SLACKEN THIS AFTERNOON AND WINDS SHOULD DIMINISH.
PATCHY LIGHT SPRINKLES PERSIST OVER THE FAR NRN CWA EARLY THIS
MORNING WHERE LOW LEVEL MOISTURE IS POOLING ALONG THE 925-850 MB
TROUGH... BUT THIS MASS CONVERGENCE WILL DECREASE THIS MORNING AND
WILL TREND OUT THESE PATCHY SPRINKLES TOWARD A DRY FORECAST.
SCATTERED (OCCASIONALLY BROKEN ACROSS THE NORTHERN AND NE CWA)
STRATOCUMULUS CLOUDS ARE EXPECTED AT THE TOP OF THE MIXED LAYER FROM
MIDDAY INTO THE AFTERNOON... YIELDING PARTLY TO MOSTLY SUNNY SKIES.
HIGHS 67-72 FIT WILL WITH LOW LEVEL THICKNESSES AND AN AVERAGE OF
STATISTICAL GUIDANCE. EXPECT CLEAR SKIES TONIGHT WITH DIMINISHING
WINDS AS WEAK HIGH PRESSURE NOW OVER THE GREAT LAKES REGION BUILDS
IN FROM THE NNW. LOWS 42-47. -GIH
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY/...
AS OF 255 AM WEDNESDAY...
FOR THURSDAY: A PLEASANT AND WARM DAY. WEAK SURFACE HIGH PRESSURE
SITS OVERHEAD... AND MODELS AGREE ON DRY AND STABLE AIR IN PLACE
THROUGH THE COLUMN WITH A FLAT FLOW ALOFT IN THE WAKE OF THE QUICKLY
DEPARTING AND DISSIPATING SHORTWAVE TROUGH TO OUR NE. EXPECT PLENTY
OF SUNSHINE... AND AS THICKNESSES WARM SLIGHTLY FROM TODAY... HIGHS
SHOULD REACH INTO THE 72-76 RANGE.
FOR THURSDAY NIGHT/FRIDAY: THE ELONGATED NEGATIVELY TILTED MID LEVEL
TROUGH STRETCHING FROM OFF THE BC COAST TOWARD CO/NM EARLY THURSDAY
IS STILL EXPECTED TO CLOSE OFF A POTENT LOW OVER KS BY THURSDAY
EVENING... RESULTING IN WEAK BROAD RIDGING UPSTREAM FROM THE GREAT
LAKES TO THE SOUTHEAST STATES. THE WEAK HIGH OVERHEAD SHIFTS TO OUR
EAST BUT BECOMES OVERTAKEN BY A STRONGER (AND COOLER) RIDGE CENTERED
WELL TO OUR NORTH OVER JAMES BAY. THE MODELS DIFFER SLIGHTLY ON
WHETHER OR NOT THIS IS TRULY A BACKDOOR FRONTAL ZONE DROPPING INTO
NRN AND NE NC FROM THE NORTH... AS THE GFS SHOWS A MARKED DROP IN
BOUNDARY LAYER THETA-E INTO THE NRN AND ERN CWA ON FRIDAY ALONG WITH
A STRONGER PUSH OF HIGHER PRESSURES FROM THE NORTH AS COMPARED TO
THE NAM. THE GFS'S RESULTING STRONGER 850 MB FLOW FROM THE ESE DOES
BRING IN A FEW MORE STRATOCUMULUS ON FRIDAY MORNING... AND ITS
SLIGHTLY FASTER EASTWARD MOVEMENT OF THE KS VORTEX INTO MO FRIDAY
ALLOWS THE MID/HIGH CLOUDS TO SPREAD EASTWARD INTO NC MUCH FASTER.
WITH NO CLEAR WINNER HERE AND ONLY MINOR DIFFERENCES WITH RESPECT TO
OUR SENSIBLE WEATHER... WILL SHOW A SLOW BUT STEADY INCREASE IN
CLOUDS WEST TO EAST FRIDAY... WITH TEMPS SIMILAR TO THURSDAY'S
HIGHS... BUT WILL NUDGE THEM DOWN A DEGREE OR TWO IN THE NORTHEAST
AS A NOD TOWARD THE POSSIBILITY OF A SLIGHTLY COOLER/DRIER AIR MASS
WORKING IN HERE FROM THE NORTH. -GIH
&&
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 310 AM WEDNESDAY...
PACIFIC JET ENERGY DIGGING ACROSS THE ROCKIES WILL DEEPEN A SYSTEM
FROM THE LEE OF THE ROCKIES TO THE MID MS RIVER VALLEY REGION ON
FRIDAY. THERE HAS BEEN GOOD GENERAL AGREEMENT BETWEEN THE GFS/ECMWF
ON AN UPPER WAVE CUTTING OFF AND THE SYSTEM BECOMING VERTICALLY
STACKED AS THE A ~995MB SURFACE LOW LIFTS NE FROM MO TO THE
GREAT LAKES BY SATURDAY MORNING. AN ONGOING QLCS FRIDAY IN A
MODERATELY UNSTABLE AIRMASS OVER THE DEEP SOUTH...FURTHER SUPPORTED
BY THE SURFACE COLD FRONT/PREFRONTAL TROUGH AND INCREASINGLY
DIFLUENT UPPER LEVEL FLOW AS A SPEED MAX SURGES INTO THE BASE OF THE
UPPER LOW...SHOULD BE APPROACHING THE SOUTHERN APPALACHIANS BY 06Z
SATURDAY. MODELS HAVE SLOWED ARRIVAL TIME OF THE CONVECTIVE LINE BY
6-12 HOURS...MORE TOWARD THE DAYTIME HOURS SATURDAY. THIS MAY SPELL
A GREATER SEVERE THREAT AS MODEST DESTABILIZATION WILL BE POSSIBLE
VIA DAYTIME HEATING AND A SURGE OF 60F+ DEWPOINT AIR FROM THE SOUTH.
AS THE UPPER TROUGH BECOMES NEGATIVELY TILTED...DEEP LAYER SHEAR IN
EXCESS OF 50KT AND AND LOW LEVEL VEERING PROFILE/HODOGRAPH
SIGNATURES ARE A BIT CONCERNING. TIMING AND DESTABILIZATION WILL BE
KEY WITH THIS SYSTEM...AND THOSE DETAILS WILL HOPEFULLY BECOME MORE
CLEAR IN SUBSEQUENT FORECASTS. GIVEN THE AMOUNT OF MID LEVEL
FORCING AND STRENGTH OF THE LOW LEVEL JET... RELATIVELY QPF AMOUNTS
ARE FORECAST TO RANGE FROM 0.5-1.0" ON AVERAGE...WITH HIGHER AMOUNTS
CERTAINLY POSSIBLE.
AS FOR TEMPS....WIDESPREAD MID AND HIGH CLOUDS WILL BE POSSIBLE AS
THE SYSTEM APPROACHES SATURDAY...BUT MILD MID 60 LOWS SATURDAY
MORNING AND PREFRONTAL WARM ADVECTION SHOULD BE SUFFICIENT TO PUSH
HIGHS INTO THE MID TO UPPER 70S OVER THE EASTERN CWA...COOLER IN THE
WEST WITH EARLIER ARRIVAL OF PRECIP.
AS THE SYSTEM DEPARTS THE REGION LATE SATURDAY...MODELS INDICATE A
BRIEF PERIOD OF ZONAL FLOW ALOFT WHILE SURFACE HIGH PRESSURE BUILDS
QUICKLY ACROSS THE SOUTHERN US TO THE CAROLINA COAST BY MONDAY.
TEMPS AROUND NORMAL SUNDAY WILL BEGIN TO REBOUND BACK ABOVE NORMAL
MONDAY AND TUESDAY AS SOUTHWESTERLY FLOW ALOFT DEVELOPS AHEAD OF THE
MEAN TROUGH BECOMING ESTABLISHED OVER THE CENTRAL US. THERE AS SOME
LONGWAVE AMPLIFICATION DIFFERENCES AMONG MEDIUM RANGE MODELS...
WHICH LEADS TO LESS CONFIDENCE IN WHEN THE NEXT SYSTEM WILL IMPACT
CENTRAL NC...AND A SLOWER APPROACH PER ECMWF WOULD NOT BRING POPS IN
UNTIL LATE WEDNESDAY OR THURSDAY.
&&
.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
AS OF 150 AM WEDNESDAY...
EXPECT VFR CONDITIONS THROUGH TONIGHT. CURRENT CIGS WITH BASES ABOVE
5 THOUSAND FEET WILL PERSIST OVER THE NORTHERN TERMINAL FORECAST
SITES (INT/GSO/RDU/RWI) UNTIL AROUND DAYBREAK. THESE ARE ASSOCIATED
WITH AN UPPER LEVEL LOW PRESSURE AREA CENTERED JUST TO OUR NORTH
OVER VA. AS THIS LOW DRIFTS TOWARD THE NNE AND AWAY FROM THE AREA
TODAY... SKIES WILL GRADUALLY CLEAR OUT WITH UNRESTRICTED SKIES AND
VSBYS INTO TONIGHT AS WEAK HIGH PRESSURE BUILDS INTO THE AREA FROM
THE NW. WINDS WILL HOLD FROM THE NW TODAY (AND WILL VEER TO NWRLY AT
RDU/RWI/FAY) AT SPEEDS OF 8-13 KTS WITH OCCASIONAL GUSTS TO 15-20
KTS FROM 13Z-22Z... MAINLY AT INT/GSO. WINDS BECOME LIGHT FROM THE
NORTH THIS EVENING.
LOOKING BEYOND 06Z EARLY THURSDAY MORNING... VFR CONDITIONS WILL
DOMINATE THROUGH FRIDAY WITH HIGH PRESSURE NOSING IN FROM THE NW
THEN NORTH. AN APPROACHING STORM SYSTEM FROM THE WEST WILL BRING
THICKENING AND LOWERING MID CLOUDS AND LOW IFR STRATUS STARTING
FRIDAY EVENING WITH AN INCREASING RISK OF LOW LEVEL WIND SHEAR. GOOD
CHANCE OF IFR CIGS WITH WIDESPREAD SHOWERS AND STORMS SATURDAY...
THEN IMPROVING CONDITIONS BACK TO VFR ON SUNDAY. -GIH
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...SMITH
NEAR TERM...HARTFIELD
SHORT TERM...HARTFIELD
LONG TERM...SMITH
AVIATION...HARTFIELD